These figures come from the 2011 census - try another squirm-out as this one doesn't work!
Actually, Owl, I think you'll find - from your own OP - that they date from 2014.
However, that is irrelevant, because although the vast majority of people in the UK have traditionally aligned themselves with either Christian or CoE when filling in census and social attitude forms, we don't really know how many of them were actually answering the question correctly. If, as has been pointed out several times on this board, the number of people who attend church is a better figure to work with, it means that thousands (maybe millions) of British people have potentially - perhaps unwittingly - been perjuring themselves when completing such forms (iirc, it is illegal to give false information at least when responding to the census though its not illegal not to complete it).
As I've mentioned at least once before, the figures that accompanied the Welsh Revival of 1904-05 suggest that nowhere near 100% of the Welsh people were believers prior to the revival. The reports of the time suggest around 100,000 conversions in, mostly, South Wales. That would have been about 10% of the South Wales population and about 7% of the total Welsh population (2,033,287 in the 1901 census). I doubt that all the non-believers in the country converted in that 12-14 month period.
It is very easy to use the church attendance figures as an indicator of the number of believers (realistically, it probably gives an upper limit to that figure) but we have absolutely no idea of how many of those attending prior to the late 40s did so out of a sense of social duty/tradition/habit and how many did so out of conviction. Even today, no-one truly counts the believers as opposed to the attendees. The BSA surveys get closest, but since the first of these took place in the early 80s, it is hard to know what the figures were prior to 1983. Equally, what does a 'belief in a God' mean to most people; what does the term 'religion' mean? In years gone past, I have often put myself in the category of 'of no religion' because I don't see Christianity as traditionally religious. Churchianity (
loyalty to the church rather than Christianity http://www.collinsdictionary.com) may well be, but the two are very different.